Linear and non-linear viscoelastic behaviour of natural rubber composites from micro- to nanoscales

Natural rubber has continued to be widely used because of its mostly elastic properties when crosslinked, compared with viscoelastic and irreversible viscous properties of highly filled and blended compositions. It has a wide linear viscoelastic window with low hysteresis. Deviation from ideal elastomer behaviour occurs at low extensions on first extension and at high extensions due to fully extended molecular segments between crosslinks and crystallization of fully extended segments. Natural rubber is adaptable through crosslink density, blending with other polymers and addition of fillers, with carbon black and silica being most important. Nanofillers offer greater adaption at small volume fractions with variation of geometry, surface area and coupling agents at the interface. Fillers create non-linear viscoelastic response through interaction with chain segments and filler-filler agglomeration that can be reversible when the composite is strained. This chapter reviews modification of viscoelastic character of natural rubber by formation of nanocomposites that further extend its exceptional deformation and thermodynamic response.